The talk doesn't mean the US is on the verge of extending its air campaign against Islamic State fighters into Syria, or shifting from an adversarial to cooperative stance with Syrian leader Assad in the interest of defeating IS.

Washington — President Obama says the United States will be “relentless” in going after the Islamic State, the militant organization that brutally executed American James Foley this week and whose advances in northern Iraq from its base in Syria prompted the president to order airstrikes earlier this month.

But that does not mean the US is on the verge of extending its air campaign against IS fighters into Syria, or swallowing hard and shifting from an adversarial to cooperative stance with Syrian leader Bashar al-Assad in the interest of defeating IS – two steps that some regional experts and prominent former officials are advocating.

Instead, Mr. Obama appears set to stick with a two-step strategy that abides by his deep reluctance to plunge the US military into Syria.

That plan envisions first reversing the IS threat to American personnel and interests and to Iraqi minorities in northern Iraq and containing the group in the short term. That effort is already under way.

More long term, the US will move to defeat IS – also known as ISIS or ISIL, the administration’s preferred acronym for the group – but only in conjunction with the local forces whom the US will expect to take the lead on the ground: the Iraqi military and Kurdish peshmerga in Iraq, and the moderate rebel forces in Syria that the US is beginning to arm.

That scenario emerged from comments that Obama’s deputy national security adviser, Ben Rhodes, made Friday afternoon to reporters at the president’s vacation on Martha’s Vineyard.

“Absolutely in the long term we want to see an organization like ISIL defeated,” Mr. Rhodes said, after defining Obama’s “strategy” for confronting IS in Iraq with three terms: evict, squeeze, and push out.

The more near-term objective is to “evict” IS fighters from the territory they have grabbed in recent weeks as they have advanced toward Iraqi Kurdistan, he said, then to “squeeze them” back into a contained area. “Ultimately” the aim will be to “push them out of that space,” he added, with the US backing the Iraqi and peshmerga forces on the ground.

“This is going to have to be a team effort,” he said.

The White House comments came a day after Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff and the president’s senior military adviser, said in public comments that IS “will eventually have to be defeated.”

To do that, he added, will require “addressing that part of the organization that resides in Syria.”

General Dempsey further said defeating IS “requires the application of all the tools of national power,” ranging from diplomatic to military, and “only one small part of which is airstrikes.”

Yet despite administration officials’ talk of “defeating” IS, some national security experts say they are not sure the president is signaling he is ready to do what would be necessary to defeat a group that some are calling a bigger threat than Al Qaeda.

“The president doesn’t seem yet to be committed to taking this on, particularly the Syria piece of it,” says Peter Feaver, director of the Triangle Institute for Security Studies at Duke University in Durham, N.C., and a former adviser for strategic planning on the National Security Council staff of President George W. Bush.

Defeating IS necessarily means “broadening and lengthening the fight” by going into Syria, Mr. Feaver says – otherwise the Islamist militants put under pressure in Iraq could just “flee across the border” into Syria. That would repeat what happened with the Afghan Taliban in the fall of 2001, he says, “when they were defeated inside Afghanistan but were able to flee into Pakistan.”

Rhodes did say in his comments, "We're not going to be restricted by borders" in protecting Americans from IS.

In addition, Feaver says, expanding the fight against IS into Syria would very likely require some US military personnel on the ground, even if limited to advisers and some special forces to assist the Syrian moderate rebels whom the administration is talking about working with.

“Whether the Syrian [rebel] units are up for that task is an open question, so I think you’d need a pretty substantial advisory capacity at a minimum,” he says. “What that means is that the president’s ‘no boots on the ground’ will probably have to be relaxed.”

Such reasoning is what has some intervention skeptics warning of signs of “mission creep” in administration officials’ talk of defeating and even “destroying” (Secretary of State John Kerry) IS.

But others say such fears are overstated and insist that the US could take steps that deal heavy blows to IS without getting bogged down in Syria.

“I think what Dempsey was saying is that you want to get their leadership, and if you want to decapitate these guys, their main headquarters are in Syria, so eventually you’d have to hit them there,” says Lawrence Korb, a former Pentagon official now at the Center for American Progress (CAP) in Washington. “If you had good intel on [the leadership], you’d go after them tomorrow,” he adds, “but that’s no more mission creep than going in and trying to rescue James Foley was.”

Pentagon officials revealed after release of the video showing Mr. Foley’s murder that a rescue attempt of him and other kidnapped Americans was made earlier this summer. No captives were found at the site where Special Forces landed.

The back-to-back official comments on the strategy for taking on IS suggests that debate is ongoing among administration policymakers, analysts say, and that the president is likely to lay out his thinking – and how he plans to use what Dempsey calls a “variety of instruments” – at some point soon.

Obama is planning to convene a United Nations Security Council session in September to take up the issue of foreign fighters among the ranks of Islamist terrorists, Rhodes said Friday. The president will also consult with Congress on next US steps, he said.

One major question hanging out there is whether Obama, who for three years has insisted Mr. Assad must go, will now reverse course and seek to work with him in the interest of defeating IS, which many regional experts say is now the greater of two evils.

Rhodes answers with a categorical “no,” adding that the administration’s position remains that Assad is part of the problem that allowed IS to take hold and grow.

Indeed, some say that Assad, who insisted from the beginnings of the Syrian revolution that he was dealing with “terrorists,” cynically allowed the fighters of Al Qaeda in Iraq – which was to become ISIS, and then IS – to gain a foothold in the north and east of Syria so that the West would be forced to reduce its pressure on him in the greater interest of defeating Islamist extremism.

Some say the old truism that “the enemy of my enemy is my friend” will lead the US to align with Assad as it zeroes in on defeating IS. But others say it is Assad who has already applied the adage by realizing early on that a strong IS could be an asset.

The Obama administration’s former ambassador to Syria, Robert Ford, is warning against any tacit cooperation with Assad concerning IS. “The Assad regime is actually at best watching what the Islamic State is doing and at worst is in some way coordinating with them tactically on the ground in many instances,” Mr. Ford said in a PBS interview this week.

Feaver of Duke says the administration already accepted Assad as a “de facto” partner once, when the chemical weapons deal that the US, Russia, and Syria agreed to last fall required the three parties to work together.

But, he notes, the administration announced this week that “that deal is done,” given the removal and destruction of Syria’s CW stocks.

“The president now has a freer hand than he would have [with Assad],” Feaver says. Adding that he sees Assad as “more fearful of the moderates than he is of ISIL,” he says the US should be cautious about seeing Assad as any kind of ally. “Assad’s reliability as a partner against ISIL is very suspect,” he says.

Mr. Korb of CAP is less wary of cooperation with Assad, noting that IS’s rise has already led the US to accept a certain degree of cooperation with Iran on Iraq, and the need for Baghdad to form a unity government to push back IS in the country’s Sunni regions.

He also takes a historical view: “Remember, we joined with Stalin in World War II, and that was by the same reasoning we’re hearing now, that ISIL is a greater threat to us than Assad.”